Digital multimeter with automatic measurement selection function

Abstract

A digital multimeter comprising a measured object input terminal, conversion circuit for a fast analog/digital converter, microprocessor, auxiliary program-controlled voltage or current source, potential divider network, electronic switches, and display. Compared with conventional multimeters, the adoption of fast analog/digital conversion technology as well as a method that applies an auxiliary power supply at the time of a passive analog measurement allows for measuring different responses between input terminals after an auxiliary power supply is applied, thus being able to automatically determine the characteristics and size of the measured object.

1. A digital multimeter for automatically selecting measurement functions comprising:
 input terminals of a measured object; 
 an analog/digital conversion circuit; 
 a microprocessor; 
 a potential divider network; 
 an electronic switch; 
 a display; and 
 a fast analog/digital converter; 
 wherein, said fast analog/digital converter is connected to said input terminal of the measured object by said potential divider network to obtain a fast measurement of the voltage between said input terminals; 
 said analog/digital conversion circuit inputs said fast measurement of the voltage into said microprocessor for analysis and processing, said microprocessor controls said electronic switch to switch said potential divider network by including additional resistances into said potential divider network and choose a measuring range for the fast analog/digital converter; 
 said microprocessor controls an auxiliary program-controlled voltage and current source in connection with the input terminals of the measured object and, according to a result of voltage variations by said fast analog/digital converter, choose a measurement method and the measuring range for the fast analog/digital converter; 
 when said auxiliary program-controlled voltage and current source is actively applied to the measured object at the input terminal, the connection between said program-controlled voltage or current source controlled by the microprocessor and said input terminal is cut off; 
 when said auxiliary program-controlled voltage and current source is passively applied to the measured object at the input terminal, the connection between the said program-controlled voltage or current source controlled by the microprocessor and said input terminal is connected; 
 said microprocessor controls the display to show a measured value. 
 
     
     
       2. The digital multimeter for automatically selecting measurement functions of  claim 1 , wherein,
 said microprocessor automatically judges whether the measured object provides a DC or an AC signal according to the data output by the fast analog/digital converter when detecting an external voltage, and the microprocessor determines the measured result by analysis and processing. 
 
     
     
       3. The digital multimeter for automatically selecting measurement functions of  claim 1 , wherein,
 when no external voltage is detected at said input terminal, an auxiliary program-controlled voltage or current source is input to the input terminal by said microprocessor; the fast analog/digital converter inputs the measured result into the microprocessor for analysis, which can judge what analog quantity the measured object connected between the input terminals delivers, and the microprocessor properly processes the result measured by the fast analog/digital converter and the microprocessor determines the measurement result by choosing a properly auxiliary program-controlled source to act on the measured object. 
 
     
     
       4. The digital multimeter for automatically selecting measurement functions of  claim 1 , wherein,
 said program-controlled voltage or current source controlled by said fast analog/digital converter and said microprocessor selects multiple analog measurements and a measurement range. 
 
     
     
       5. The digital multimeter for automatically selecting measurement functions of  claim 4 , wherein,
 when measuring said passive analog quantity of the object, a micro test current is output first to apply to the input terminal a circuit with high input impedance. 
 
     
     
       6. The digital multimeter for automatically selecting measurement functions of  claim 1  further comprising a selection button for switching between automatic selection of measurement functions and manual selection of measurement functions by a user. 
     
     
       7. The digital multimeter for automatically selecting measurement functions of  claim 1 , wherein said microprocessor can display a waveform graph of a signal that varies with time and a graph of a value variation over time using storing partial measurement data.